Net Thermal Radiation Under Shading Screens

Teitel, M.; Segal, I.

doi:10.1006/jaer.1995.1026

Cited by 17 publications

(5 citation statements)

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“…Shading screens can also be effective in reducing the risk of frost damage (Teitel & Segal, 1995;Teitel et al, 1996) and eliminating the problem of thermal inversion. These problems occur on clear nights when a large amount of radiant heat is sent back to the sky.…”

Section: Introductionmentioning

confidence: 99%

Shading screens for the improvement of the night time climate of unheated greenhouses

Montero¹,

Muñoz²,

Sánchez-Guerrero

et al. 2013

Span. j. agric. res.

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The objective of this work was to study the effect of shading screens, normally used during the day for cooling purposes, on the night-time climate of unheated greenhouses. For this purpose, first a number of experimental measurements were taken during cold nights to characterise the greenhouse climate both with and without an aluminised external screen. Secondly a Computational Fluid Dynamic (CFD) model of greenhouse was developed. After validation of the model by comparison with experimental data, the model was used to simulate the greenhouse climate for different sky conditions ranging from cloudless to overcast nights. Simulations were performed for a greenhouse with internal and external shading screens and for the same greenhouse without screens. Experimental results showed the positive effect of an external shading screen, whose use increased night-time temperature and reduced the risk of thermal inversion. Its effect was much stronger under clear sky conditions. The CFD model supported this conclusion and provided a detailed explanation of the temperature behaviour of all the greenhouse types considered. CFD simulations proved that an aluminised screen placed inside the greenhouse at gutter height gave the greatest thermal increase. Therefore, external or internal screens can help to increase the sustainability of greenhouse production in areas with mild winter climates by enhancing the use of solar energy stored in the greenhouse soil during the previous day and released at night-time.

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Section: Introductionmentioning

confidence: 99%

Shading screens for the improvement of the night time climate of unheated greenhouses

Montero¹,

Muñoz²,

Sánchez-Guerrero

et al. 2013

Span. j. agric. res.

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“…Outgoing radiation from a surface with nonzero transmissivity cover and sidewalls can be described in Eq. 8 [23]:…”

Section: Conduction Energy Transfer Processmentioning

confidence: 99%

CFD Simulation of Heat and Mass Transfer for Climate Control in Greenhouses

Rodriguez¹,

Velázquez²

2019

Heat and Mass Transfer - Advances in Science and Technology Applications

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Greenhouse plant production involves a number of processes such as transpiration, condensation, photosynthesis, and climate control. Such processes, in turn, set off mass and heat transfer phenomena that influence not only the quality and quantity of crop production but also its environmental cost. While these processes have considerably been analyzed in separate, they strongly interact with one another. For instance, increased radiation (mainly thermal infrared) increases temperature, reduces humidity, consequently increases transpiration, and affects CO 2 exchange as well as other reaction rates. Computational fluid dynamics (CFD) is a numerical tool with a solid physical basis which allows, through the construction of a computational model, to simulate the fluid flow environment. Heating, ventilation, and condensation have been analyzed in the greenhouse environment with CFD techniques. The current challenge is the interaction of these processes and their impact on the production system. The present work summarizes some CFD investigations carried out in this topic, in order to analyze the processes of heat and mass transfer in a greenhouse for agronomic purposes.In greenhouse crop production, climate has peculiar considerations, because the most important data is the impact of the environmental factors on the crop cycle. The cultivation of plants requires a sufficient amount of light, a specific range of temperature, humidity, and CO 2 , among other requirements. These requirements are primarily influenced by the greenhouse design and size and vary according to the local climate conditions. For instance, the radiation quantity inside the greenhouse depends on whether greenhouses are built with PVC or glass, because the surface material is the element to optimally use solar radiation for the required lighting [1].Recently, heating, ventilation, and air conditioning (HVAC) systems have been extensively used in urban spaces, such as offices or stores, at agriculture area, and specifically in greenhouses. For instance, HVAC has been used in buildings in order to analyze the optimization and comfort inner Officine's and several uses. In greenhouses, the concept is incipient, even though the application of the ventilation and calefaction systems as a method to climate control in cold and warm regions is nothing new.The climate produced in a greenhouse is the result of complex mechanisms involving the processes of heat and mass exchange. The internal climate is strongly dependent on the outside conditions, especially in unheated greenhouses. In greenhouse climate models, the parameters of the internal climate such as air, soil, and crop temperatures as well as air humidity are calculated using energy and water vapor balances for the various components of the system [2].Climate in the greenhouse is a consequence of radiation crossing the cover material, usually plastic. After that, climate condition is a strong relationship between several factors, temperature, humidity, wind velocity, and the solar radiation. Environ...

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“…Thermal screens mainly decrease heat transfer rate in an environment and offer an additional thermal resistance (Arinze et al, 1986). Aluminum thermal screens reduce radiation conductivity (Teitel and Segal, 1995). Thermal screens can help save energy in greenhouses.…”

Section: Introductionmentioning

confidence: 99%

The Experimental Determination of The Impact of Overall Heat Consumption Coefficient and Thermal Screens on Heat Saving in Plastic Greenhouses

Çayli

Akyüz

2019

Kahramanmaraş Sütçü İmam Üniversitesi Tarım Ve Doğa Dergisi

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This study was conducted to experimentally determine the effect of thermal screens used for heat saving and overall heat consumption coefficient on heat loss in greenhouses. The trial was established in three different lettuce greenhouses with 150 m 2 in floor size using different plastic covering materials between January and April. Hot air vent heaters were used for heating. The heaters were positioned 30 cm above ground level. The heating was done between 08.00 p.m. and 05.00 a.m. Plant level and roof level as well as external temperature and relative humidity were measured with data loggers. These measurements were used to statistically calculate overall heat consumption coefficient based on wind speed. The results demonstrate that thermal screens created a resistance against heat loss, thus reducing heat losses. The effect of thermal screens on heat loss depending on the wind speed was also determined. It was found out that heat saving ratios in greenhouses varied between 8% to 22% under very low wind speeds and between 17%-36% under a wind speed of 4 m s-1 .

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Net Thermal Radiation Under Shading Screens

Cited by 17 publications

References 0 publications

Shading screens for the improvement of the night time climate of unheated greenhouses

Shading screens for the improvement of the night time climate of unheated greenhouses

CFD Simulation of Heat and Mass Transfer for Climate Control in Greenhouses

The Experimental Determination of The Impact of Overall Heat Consumption Coefficient and Thermal Screens on Heat Saving in Plastic Greenhouses

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